CN103869136B - A kind of radio-frequency measurement device - Google Patents

Abstract

The present invention provides a radio frequency measuring device, comprising: a frequency synthesizer circuit, an automatic level control circuit and a step attenuation circuit, wherein the automatic level control circuit comprises a variable attenuator, an amplifier, a coupler, a peak detector and a comparator; Also includes: a control module, a first D/A converter, a second D/A converter, a first resistor, a second resistor and an adder; the signal output by the frequency synthesizer circuit passes through the variable attenuator, the amplifier and the coupling in sequence The output signal generated by the output signal is given to the step attenuation circuit, and the peak detector converts the power value of the output signal into a voltage value and outputs it to the comparator; an input signal passes through the control module, the first D/A converter, and the second input signal respectively. The circuit where the first resistor is located and the control module, the second D/A converter, and the circuit where the second resistor is located enter the adder to generate a reference voltage, and the reference voltage and voltage value generate a differential pressure value in the comparator and enter the variable attenuator .

Description

A radio frequency measuring device

technical field

The invention relates to the technical field of measurement and testing, in particular to a radio frequency measurement device.

Background technique

A radio frequency measurement device is a device that outputs radio frequency signals with high frequency resolution, accuracy, and high amplitude accuracy. The frequency range of its output signal usually ranges from several kHz to several GHz; the signal source has a wide range of amplitude output, usually can From -130dBm or lower to +20dBm or higher. It is used in communication, education, military and other fields.

As shown in Figure 1, the radio frequency measurement device mainly includes: a frequency synthesizer circuit 101, an automatic level control (Automatic Level Control ALC) circuit 102 and a step attenuation circuit 103, the frequency synthesizer circuit 102 processes the input signal and outputs the required After passing through the automatic level control circuit 102, the frequency signal with constant amplitude is output, and then the set signal amplitude is obtained after passing through the step attenuator circuit 103.

FIG. 2 is a block diagram of a prior art automatic level control circuit. The automatic level control circuit includes: variable attenuator 201 , amplifier 202 , coupler 203 , peak detector 204 , grounding resistor R, comparator 205 , D/A converter 206 and control unit 207 .

The peak detector 204 converts the power of the output signal through the coupler 203 into a voltage, compares it with a given reference voltage, and the obtained voltage difference controls the variable attenuator 201, and after the amplifier 203, the automatic level control circuit The output power eventually reaches a steady state. Wherein, the generation process of the reference voltage is: the theoretical output value of the radio frequency measuring device and the attenuation value of the amplitude attenuation module generate the theoretical output value of the automatic control circuit through the control unit 207, and pass through the D/A converter 206 as the reference voltage.

The change of the attenuation of the variable attenuator 201 is controlled by the output voltage of the comparator 205 , and the resolution of the voltage is determined by the D/A converter 206 at the input end of the comparator 205 . When the number of bits of the D/A converter 206 is determined, the resolution of the attenuation change of the variable attenuator 201 is limited, that is, the resolution of the output power of the automatic level control circuit is limited.

Contents of the invention

The invention provides a radio frequency measuring device to eliminate the limitation of the output power resolution of the automatic level control circuit and improve the resolution of the output power of the automatic level control circuit.

In order to achieve the above object, the present invention provides a radio frequency measuring device, including: a frequency synthesizer circuit, an automatic level control circuit and a step attenuation circuit, and the automatic level control circuit includes a variable attenuator, an amplifier, and a coupler , a peak detector and a comparator, the automatic level control circuit also includes: a control module, a first D/A converter, a second D/A converter, a first resistor, a second resistor and an adder; The signal output by the frequency synthesizer circuit passes through the variable attenuator, the amplifier and the coupler successively to generate an output signal, and the peak detector converts the power value of the output signal into a voltage value and outputs it to the comparator; An input signal respectively passes through the circuit where the control module, the first D/A converter, and the first resistor are located, and the circuit where the control module, the second D/A converter, and the second resistor are located, and then enters the addition A reference voltage is generated after the comparator, and the reference voltage and the voltage value generate a pressure difference value in the comparator and enter the variable attenuator to perform amplitude calibration on the automatic level control circuit.

Further, the resistance values of the first resistor and the second resistor are different.

Further, the control module is an FPGA or a single-chip microcomputer.

Further, the control module includes: a first control module connected to the first D/A converter; a second control module connected to the second D/A converter.

Further, when performing amplitude calibration on the automatic level control circuit, the first D/A converter is fixed at the middle position, and the value of the second D/A converter is adjusted from small to large, according to The output data of the automatic level control circuit calculates the value of the second D/A converter by linear interpolation; if the resolution of the output power of the automatic level control circuit is less than the second D/A converter The adjustment range of the converter, select two calibration values near the output power and calculate the slope, generate the slope of the first D/A converter according to the slope and the ratio of the first resistance to the second resistance, according to The slope of the first D/A converter and the variation of the output power to calculate the value of the first D/A converter; Two D/A converters are preset.

Further, the input signal includes: the theoretical output amplitude of the automatic level control circuit obtained by calculating the theoretical output value of the radio frequency measuring device set by the user and the attenuation value of the step attenuator.

Further, the ratio of the first resistor to the second resistor is 10:1.

The beneficial effect of the embodiment of the present invention is that the radio frequency measurement device of the present invention can eliminate the limitation of the output power resolution of the automatic level control circuit by improving the design of the automatic level control circuit, and improve the resolution of the output power of the automatic level control circuit. Rate.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained according to these drawings without any creative effort. In the attached picture:

Fig. 1 is the signal channel schematic diagram of the radio frequency measuring device of prior art;

FIG. 2 is a schematic structural diagram of an automatic level control circuit in the prior art;

3 is a schematic structural diagram of an automatic level control circuit according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of an automatic level control circuit according to another embodiment of the present invention.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

An embodiment of the present invention provides a radio frequency measurement device (which may be a radio frequency signal source), including: a frequency synthesizer circuit 101 , an automatic level control circuit 102 and a step attenuation circuit 103 . Wherein, the Automatic Level Control (ALC) circuit 102 includes a variable attenuator 201 , an amplifier 202 , a coupler 203 , a peak detector 204 , a grounding resistor R and a comparator 205 .

It should be noted that the present invention is only described by using a radio frequency signal source as a radio frequency measurement device. The present invention can also be applied to radio frequency measurement devices such as spectrum analyzers and logic analyzers, such as tracking source circuits of spectrum analyzers.

As shown in Figure 3, the automatic level control circuit 102 also includes: a control module 301, a first D/A converter 302, a second D/A converter 303, a first resistor R ₁ , a second resistor R ₂ and Adder 306 .

The signal output by the frequency synthesizer circuit 101 in Fig. 1 passes through the variable attenuator 201 of the automatic level control circuit 102 successively, the amplifier 202 and the coupler 203 generate the output signal, and the peak detector 204 converts the power value of the output signal is the voltage value V1 and output to the comparator 205 .

An input signal a1 generates a signal b1 after passing through the circuit where the control module 301, the first D/A converter 302, and the _first resistor R1 are located (DAC1 Digital to analog converter for short), the input signal control module 301, the second D/A The A-converter 303 and the circuit DAC2 where the _second resistor R2 is located generate c1.

The input signal a1 is the theoretical output amplitude of the automatic level control circuit obtained by calculating the theoretical output value of the radio frequency measuring device set by the user and the attenuation value of the step attenuator. The theoretical output amplitude of the automatic level control circuit is used to adjust DAC1 and DAC2 to change the attenuation value of the variable attenuator in the automatic level control circuit. Among them, the attenuation value of the step attenuator can be set by the user, or can be obtained according to the theoretical output value of the RF measuring device, that is, there are two modes: one is auto, which is automatically set according to the theoretical output value of the RF measuring device set by the user. Obtain the attenuation value; the other is the user setting mode, which is obtained according to the user's setting.

is the theoretical output value of the RF signal source and the attenuation value of the amplitude attenuation module, and the values of the signals b1 and c1 are the theoretical output values of the automatic control circuit, because the resistance value of the resistor R1 in DAC1 is different from the resistance value _of the resistor R2 in _DAC2 , so the weights added by the two DACs are different, and the values of the signal b1 and the signal c1 are different.

The signal b1 and the signal c1 enter the adder 306 and add to generate a reference voltage, the reference voltage and the voltage value generated by the peak detector 204 generate a differential pressure value in the comparator 205, and the differential pressure value enters the variable attenuator 201 to control The automatic level control circuit performs amplitude calibration.

When the signal source amplitude is calibrated, the output power of the automatic level control circuit is calculated according to the power of the output signal of the frequency synthesizer circuit 101 in Fig. 1 and the insertion loss of the step attenuator circuit 103, and is performed with DAC1 and DAC2 in Fig. 3 adjust. An example is as follows: if the final output of the radio frequency measuring device is +10dBm, and the step attenuator circuit 103 of the subsequent stage is set to 0dB, but its insertion loss is 5dB, then the output of the automatic level control circuit should be +15dBm. This is how to calculate the required amplitude of the output of the automatic level control circuit according to the output setting, and obtain it by adjusting DAC1 and DAC2.

The different ratios of the _two resistors R1 and R2 in _Fig . 3 directly affect the amplitude calibration of the automatic level control circuit of the present invention. The size of the ratio is related to the amplitude resolution of the output of the automatic level control circuit, and the DAC with the larger resistance must meet or exceed the desired resolution. After the resistance values of these two resistors R ₁ and R ₂ are calculated, there is usually no need to adjust them. The reason is that when the present invention is designed, it will be far less than the expected resolution, and the index has a large margin. The boards are basically the same.

If R ₁ : R ₂ =A, that is to say, the resistance R ₁ is A (A is greater than 1) times of R ₂ , then the weight ratio of DAC2 and DAC1 is A, that is, when the two DACs are adjusted separately, DAC2 controls the variable attenuation The role of the attenuator is more obvious, the step is larger, and the step when DAC1 controls the variable attenuator is smaller, the ratio of the two is A:1. Example: In a certain radio frequency signal source, R ₁ =100k, R ₂ =10k, when DAC1 is fixed, when DAC2 is adjusted to change one word, the output amplitude of the automatic level control circuit will change by 0.1dB; when DAC2 is fixed, adjust DAC1 every time When changing a word, the output amplitude of the automatic level control circuit changes to 0.01dB. When calibrating the amplitude of the automatic level control circuit, assuming that the output amplitude needs to change by 0.15dB, you can adjust DAC2 by one word, and then adjust DAC1 by five words. By adding DAC1, the power resolution output by the automatic level control circuit can be increased from 0.1dB to 0.01dB.

When calibrating, if the resistance value of resistor R1 is greater than the resistance value of resistor R2, the first D/A converter 302 of DAC1 needs to be fixed in the middle position (for example, 12bit can be adjusted to 4096, and the middle value is 2048), by adjusting DAC2 The value of the second D/A converter 303 is changed from small to large, and the output value of DAC2 is recorded. When the RF measurement device needs to output a certain power, for example, when the automatic level control circuit needs to output +15dBm, the value of DAC2 is calculated by linear interpolation according to the output data of the automatic level control circuit (that is, the test data during calibration). If the automatic level control circuit needs output power resolution smaller than the adjustment range of DAC2, such as +15.01dBm, firstly take two calibration values around the value of DAC2 at +15dBm, calculate the slope, and use this slope and R ₁ / R ₂ , you can calculate the slope of DAC1, and then you can calculate how many words DAC1 needs to change when it changes by 0.01dB, and then preset DAC1 and DAC2 respectively through the control unit.

Optionally, the control module 301 may be an FPGA, a single-chip microcomputer or a combination of the two, which will not be repeated here.

In another preferred implementation, as shown in FIG. 4 , the control module 203 includes: a first control module 401 connected to the first D/A converter 302, the first control module 401 and the first D/A converter 320 and The _first resistor R1 together constitutes DAC1; the second control module 402 is connected to the second D/A converter, and the second control module 402, the _second D/A converter 303 and the first resistor R2 together constitute DAC2 .

The beneficial effect of the embodiment of the present invention is that the radio frequency measurement device of the present invention realizes the amplitude calibration of the ALC circuit through rough adjustment and fine adjustment by setting DAC1 and DAC2 in the ALC circuit, and improves the resolution of the output power of the ALC circuit.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (7)

1. a kind of radio-frequency measurement device, including：Frequency synthesizer circuit, automatic level control circuit and stepping attenuator circuit, institute The automatic level control circuit stated includes variable attenuator, amplifier, coupler, peak detector and comparator, and its feature exists In,

Described automatic level control circuit also includes：Control module, the first D/A converter, the second D/A converter, the first electricity Resistance, second resistance and adder；

The signal of the frequency synthesizer circuit output passes through variable attenuator, amplifier and coupler generation output signal successively To described stepping attenuator circuit, the performance number of the output signal is converted to magnitude of voltage and exported by described peak detector To described comparator；One input signal is respectively by the electricity where the control module, the first D/A converter, first resistor Reference is generated after entering described adder after circuit where road and the control module, the second D/A converter, second resistance Voltage, described reference voltage generate pressure difference with the magnitude of voltage in described comparator and enter described variable attenuation Device.

2. radio-frequency measurement device according to claim 1, it is characterised in that the resistance of the first resistor and second resistance It is different.

3. radio-frequency measurement device according to claim 1 or 2, it is characterised in that described control module includes：

First control module, connect the first described D/A converter；

Second control module, connect the second described D/A converter.

4. radio-frequency measurement device according to claim 3, it is characterised in that carried out to described automatic level control circuit Amplitude is more punctual, by the first described D/A converter centerlock, adjusts second D/A converter from small to large Value, according to the output data of automatic level control circuit, the value of second D/A converter is calculated by linear interpolation； If the resolution ratio of the power to be output of the automatic level control circuit is less than the adjustable range of second D/A converter, Two calibration values are chosen near the power to be output and calculate slope, according to the slope and first resistor and the second electricity The ratio of resistance generates the slope of first D/A converter, according to the slope of first D/A converter and the work(to be output The variable quantity of rate calculates the value of first D/A converter；By the control module to first D/A converter and second D/A converter carries out preset.

5. radio-frequency measurement device according to claim 4, it is characterised in that described input signal includes：User is set The reason for the automatic level control circuit that fixed radio-frequency measurement device theory output valve and the pad value of step attenuator are calculated By output amplitude.

6. the radio-frequency measurement device according to any one of claim 1-5, it is characterised in that the first resistor and second The ratio of resistance is 10:1.

7. the radio-frequency measurement device according to any one of claim 1-5, it is characterised in that described control module is FPGA or single-chip microcomputer.